PESHAWAR, Pakistan (AP) — Police say gunmen have killed two police officers assigned to protect a team of polio workers in northwest Pakistan.

Local police officer Khalid Iqbal says the two officers were attacked on Friday as they headed to the town of Swabi on a motorcycle to protect the polio workers. Swabi lies 100 kilometers (60 miles) northeast of Peshawar, the capital of Khyber Pakhtunkhwa province.

The attackers then fled the scene.

No group claimed responsibility, but Pakistani militants have killed more than a dozen polio workers and police protecting them over the past year. They accuse health workers of acting as spies for Washington and claim the polio vaccine is intended to make Muslim children sterile.

Pakistan is one of only three countries where the virus is still endemic.